IMPORTANCE OF EACH OF THE PRINCIPLES. 57 
generation, and so in intensifying the aptitudes. What, then, shall we 
say of the segregate association of individuals according to their habi- 
tudes, acquired by experimental initiation, individual repetition, social 
imitation, and other methods of accommodation opening to the differ- 
ent groups divergent methods of dealing with the environment; and 
what of the partition and election which coéperate in producing the 
segregate association, and so in intensifying the acquired adjustments? 
Did the individuals of the primitive form or forms of life possess 
powers that were in any way or in the least degree discriminative? 
Had they any power to select that which is needed and to reject that 
which is useless or detrimental? And when the environment became 
somewhat complex, had the same species power to divide, one section 
establishing close relations with one part of the environment and 
another section with another part of the environment? If the correct 
answers to these questions are in the affirmative, then from early times 
habitudinal segregation, in its two forms, partition and election, have 
had an important influence on racial segregation, and, therefore, on the 
evolution of innate aptitudes. 
In the production of segregated racial types isolation seems to be 
the most essential of the four principles, for there can be no racial 
segregation where there is no isolation, while there may be cases of 
segregation and divergence (at least for a number of generations) that 
are not at all dependent on new methods of action of any one or more 
of the other three principles. Such a case occurs when some peculiar 
variation or mutation, being transported to a position where there is 
no opportunity of crossing with other varieties, propagates its own 
peculiarity for many generations, though exposed to the same external 
conditions as the body of the species from which it has been separated. 
If, however, the isolation is continued through a long series of genera- 
tions, new formsof selection inevitably arise, and in time new forms 
of acquired character resulting from new forms of activity and new 
forms of direct stimulus from the environment; and in this way 
the initial segregation produced by the isolation is intensified by 
diverse forms of selection and by modifications resulting from estab- 
lished habits. Moreover, the acquired characters may become the 
active agency leading to new groupings of individuals, and in many 
cases these new groupings introduce, or are accompanied by, group- 
ings according to natural aptitudes and other innate endowments. 
In other words, using the terms just indicated, we start with isolation, 
which opens the way for divergent forms of selection, and the new 
forms of selection lead to new forms of partition, and these lead to 
new forms of isolation, thus establishing a circle of influences. Again, 
